Radio broadcasting is the transmission of electromagnetic radiation (radio waves) to receivers over a wide territory. Most broadcasts areaudio (sound), sometimes with embeddedmetadata. Listeners need abroadcast radio receiver to pick up these signals. "Terrestrial" broadcasts, includingAM,FM andDAB stations, originate signals from a land-based transmitter, while "satellite radio" signals originate from asatellite in Earth orbit.
Individual own programming, or are affiliated with aradio network that provides content, either inbroadcast syndication or bysimulcasting, or both. The most common transmission technologies areanalog anddigital signals. Analog radio uses one of twomodulation methods:amplitude modulation, used byAM radio, orfrequency modulation, forFM radio. A newer technique, digital radio stations, transmit using one of several differentdigital audio standards, such as DAB (Digital Audio Broadcasting),HD radio, or DRM (Digital Radio Mondiale).
Electronic distribution originated, to a limited extent, with the invention of thetelegraph. The most common example, "tickers", were primarily used to distribute stock price information. An additional subscription service was time signals. The concept of audio broadcasting was first developed after the invention of telephone. In a few locations, most commonly in Europe,telephone newspapers were established, to provide news and entertainment to subscribers. These systems had the advantage of being able to charge individual customers. However, a lack of a way to amplify signals meant that their ranges were generally limited to a single municipality.
Some early inventors foresaw wireless transmission's potential. In 1902,Nathan Stubblefield, who had developed wireless transmissions using ground conduction, envisioned that: "...any one having a receiving instrument, which would consist merely of a telephone receiver and a few feet of wire, and a signaling gong, could, upon being signaled by a transmitting station in Washington, or nearer, if advisable, be informed of weather news. Eventually it will be used for the general transmission of news of every description."[1]
Although it was quickly recognized that radio transmissions were capable of being broadcast to a scattered audience without needing connecting wires, there was skepticism about its finances. In an 1898 review of early radio transmissions, then known as "Hertzian telegraphy", a reviewer opined: "As to the practical applications, there were occasions when one wanted to 'shout to the world'—as in distributing political speeches to the Press—and for such a purpose the Hertz-wave and the coherer might be of service. But did not Prof. Lodge forget that no one wants to pay for shouting to the world on a system by which it would be impossible to prevent non-subscribers from benefiting gratuitously?".[2] Another limitation was that many countries required listeners to be licensed in order to operate a radio receiver.
The earliest radio broadcasting stations transmittedradiotelegraphy dots-and-dashes, for such things as time signals and weather reports, or provided news summaries intended for inclusion in shipboard newspapers. This had limited audiences, because of the need to understandMorse code. Because there was no way to collect fees from listeners, these stations were commonly operated by national governments. Beginning in 1904, the U.S. Navy broadcast daily time signals and weather reports, and a Canadian Marconi station in Camperdown, Nova Scotia began transmitting time signals in 1907.[3] In Europe, a station located at theEiffel Tower in Paris, France, transmitted time signals that were audible throughout the continent.[4]
Although most radio stations during the first two decades of the 1900s employed radiotelegraphic transmissions, there was also experimental development of audio transmissions, mostly using "amplitude modulation" (AM) signals. The first AM technologies included high-frequency spark, alternator, and arc transmitters. However, it was not until the development of vacuum-tube (also known as "valve") transmitters that widespread audio broadcasting became practical. In addition, most early experimenters worked to createradiotelephone systems for private communication, and few were interested in broadcasting information and entertainment to general audiences.
Early examples of audio broadcasts included:
The outbreak of World War One largely suspended the development of civilian radio. However, during this period major improvements were made in vacuum-tube technology, which went into service after the end of wartime restrictions. All of the following examples used vacuum-tube transmitters:
Effective December 1, 1921, the U.S. Department of Commerce issued regulations formally establishing a broadcasting service, and by the end of 1922, there were over 500 licensed stations.[27] Canada soon followed, and began issuing broadcasting station licenses in April 1922.[28]2MT in Great Britain began regular entertainment broadcasts in 1922, and that year theBritish Broadcasting Company was formed and given a national broadcasting monopoly. It received aRoyal Charter in 1926, making it the first national broadcaster in the world,[29][30] followed byCzechoslovak Radio and other European broadcasters in 1923.
Radio in education soon followed, and colleges across the U.S. began adding radio broadcasting courses to their curricula. Curry College in Milton, Massachusetts, introduced one of the first broadcasting majors in when the college teamed up with WLOE in Boston to have students broadcast programs.[31] By 1931, a majority of U.S. households owned at least oneradio receiver.[32]
In line toITU Radio Regulations (article1.61) eachbroadcasting station shall be classified by the service in which it operates permanently or temporarily.
Broadcasting by radio takes several forms. These includeAM andFM stations. There are several subtypes, namelycommercial broadcasting,non-commercial educational (NCE)public broadcasting andnon-profit varieties as well ascommunity radio, student-runcampus radio stations, andhospital radio stations can be found throughout the world. Many stations broadcast onshortwave bands using AM technology that can be received over thousands of miles (especially at night). For example, theBBC,VOA,VOR, andDeutsche Welle have transmitted via shortwave to Africa and Asia. These broadcasts are very sensitive to atmospheric conditions and solar activity.
Nielsen Audio, formerly known as Arbitron, theUnited States–based company that reports on radio audiences, defines a "radio station" as a government-licensed AM or FM station; an HD Radio (primary or multicast) station; an internet stream of an existing government-licensed station; one of the satellite radio channels fromXM Satellite Radio orSirius Satellite Radio; or, potentially, a station that is not government licensed.[33]
AM stations were the earliest broadcasting stations to be developed. AM refers toamplitude modulation, a mode of broadcasting radio waves by varying the amplitude of the carrier signal in response to the amplitude of the signal to be transmitted. The medium-wave band is used worldwide for AM broadcasting. Europe also uses thelong wave band. In response to the growing popularity ofFM stereo radio stations in the late 1980s and early 1990s, someNorth American stations began broadcasting inAM stereo, though this never gained popularity and very few receivers were ever sold.
The signal is subject to interference from electrical storms (lightning) and otherelectromagnetic interference (EMI).[34] One advantage of AM radio signal is that it can be detected (turned into sound) with simple equipment. If a signal is strong enough, not even a power source is needed; building an unpoweredcrystal radio receiver was a common childhood project in the early decades of AM broadcasting.
AM broadcasts occur onNorth American airwaves in themedium wave frequency range of 525 to 1,705kHz (known as the "standard broadcast band"). The band was expanded in the 1990s by adding ninechannels from 1,605 to 1,705 kHz. Channels are spaced every 10 kHz in theAmericas, and generally every 9 kHz everywhere else.
AM transmissions cannot be ionosphericpropagated during the day due to strong absorption in theD-layer of the ionosphere. In a crowded channel environment, this means that the power of regional channels which share a frequency must be reduced at night or directionally beamed in order to avoid interference, which reduces the potential nighttime audience. Some stations have frequencies unshared with other stations in North America; these are calledclear-channel stations. Many of them can be heard across much of the country at night. During the night, absorption largely disappears and permits signals to travel to much more distant locations via ionospheric reflections. However, fading of the signal can be severe at night.
AM radio transmitters can transmit audio frequencies up to 15 kHz (now limited to 10 kHz in the US due to FCC rules designed to reduce interference), but most receivers are only capable of reproducing frequencies up to 5 kHz or less. At the time that AM broadcasting began in the 1920s, this provided adequate fidelity for existing microphones, 78 rpm recordings, and loudspeakers. The fidelity of sound equipment subsequently improved considerably, but the receivers did not. Reducing the bandwidth of the receivers reduces the cost of manufacturing and makes them less prone to interference. AM stations are never assigned adjacent channels in the same service area. This prevents the sideband power generated by two stations from interfering with each other.[35]Bob Carver created anAM stereo tuner employingnotch filtering that demonstrated that an AM broadcast can meet or exceed the 15 kHz baseband bandwidth allotted toFM stations without objectionable interference. After several years, the tuner was discontinued. Bob Carver had left the company and the Carver Corporation later cut the number of models produced before discontinuing production completely.[36]
As well as on the medium wave bands, amplitude modulation (AM) is also used on theshortwave andlong wave bands. Shortwave is used largely for national broadcasters, international propaganda, orreligious broadcasting organizations. Shortwave transmissions can have international or inter-continental range depending on atmospheric conditions.[37] Long-wave AM broadcasting occurs in Europe, Asia, and Africa. Theground wave propagation at these frequencies is little affected by daily changes in the ionosphere, so broadcasters need not reduce power at night to avoid interference with other transmitters.
FM refers tofrequency modulation, and occurs onVHF airwaves in the frequency range of 88 to 108MHz everywhere exceptJapan andRussia. Russia, like the formerSoviet Union, uses 65.9 to 74 MHz frequencies in addition to the world standard. Japan uses the 76 to 90 MHz frequency band.
Edwin Howard Armstrong invented wide-band FM radio in the early 1930s to overcome the problem ofradio-frequency interference (RFI), which plagued AM radio reception. At the same time, greater fidelity was made possible by spacing stations further apart in theradio frequency spectrum. Instead of 10 kHz apart, as on the AM band in the US, FM channels are 200 kHz (0.2 MHz) apart. In other countries, greater spacing is sometimes mandatory, such as in New Zealand, which uses 700 kHz spacing (previously 800 kHz). The improved fidelity made available was far in advance of the audio equipment of the 1940s, but wide interchannel spacing was chosen to take advantage of the noise-suppressing feature of wideband FM.
Bandwidth of 200kHz is not needed to accommodate an audio signal — 20 kHz to 30 kHz is all that is necessary for a narrowband FM signal. The 200 kHz bandwidth allowed room for ±75 kHz signal deviation from the assigned frequency, plus guard bands to reduce or eliminate adjacent channel interference. The larger bandwidth allows for broadcasting a 15 kHz bandwidth audio signal plus a 38 kHzstereo "subcarrier"—a piggyback signal that rides on the main signal. Additional unused capacity is used by some broadcasters to transmit utility functions such as backgroundmusic for public areas,GPS auxiliary signals, or financial market data.
The AM radio problem of interference at night was addressed in a different way. At the time FM was set up, the available frequencies were far higher in the spectrum than those used for AM radio - by a factor of approximately 100. Using these frequencies meant that even at far higher power, the range of a given FM signal was much shorter; thus its market was more local than for AM radio. The reception range at night is the same as in the daytime. All FM broadcast transmissions are line-of-sight, and ionospheric bounce is not viable. The much larger bandwidths, compared to AM and SSB, are more susceptible to phase dispersion. Propagation speeds are fastest in the ionosphere at the lowest sideband frequency. The celerity difference between the highest and lowest sidebands is quite apparent to the listener. Such distortion occurs up to frequencies of approximately 50 MHz. Higher frequencies do not reflect from the ionosphere, nor from storm clouds. Moon reflections have been used in some experiments, but require impractical power levels.
The original FM radio service in the U.S. was theYankee Network, located inNew England.[38][39][40] Regular FM broadcasting began in 1939 but did not pose a significant threat to the AM broadcasting industry. It required purchase of a special receiver. The frequencies used, 42 to 50 MHz, were not those used today. The change to the current frequencies, 88 to 108 MHz, began after the end ofWorld War II and was to some extent imposed by AM broadcasters as an attempt to cripple what was by now realized to be a potentially serious threat.
FM radio on the new band had to begin from the ground floor. As a commercial venture, it remained a little-used audio enthusiasts' medium until the 1960s. The more prosperous AM stations, or their owners, acquired FM licenses and often broadcast the same programming on the FM station as on the AM station ("simulcasting"). The FCC limited this practice in the 1960s. By the 1980s, since almost all new radios included both AM and FM tuners, FM became the dominant medium, especially in cities. Because of its greater range, AM remained more common in rural environments.
Pirate radio is illegal or non-regulated radio transmission. It is most commonly used to describe illegal broadcasting for entertainment or political purposes. Sometimes it is used for illegal two-way radio operation. Its history can be traced back to the unlicensed nature of the transmission, but historically there has been occasional use of sea vessels—fitting the most common perception of a pirate—as broadcasting bases.Rules and regulations vary largely from country to country, but often the term pirate radio describes the unlicensed broadcast of FM radio, AM radio, or shortwave signals over a wide range. In some places, radio stations are legal where the signal is transmitted, but illegal where the signals are received—especially when the signals cross a national boundary. In other cases, a broadcast may be considered "pirate" due to the type of content, its transmission format, or the transmitting power (wattage) of the station, even if the transmission is not technically illegal (such as a webcast or an amateur radio transmission). Pirate radio stations are sometimes referred to as bootleg radio or clandestine stations.
Digital radio broadcasting has emerged, first inEurope (theUK in 1995 andGermany in 1999), and later in the United States, France, the Netherlands, South Africa, and many other countries worldwide. The simplest system is named DAB Digital Radio, forDigital Audio Broadcasting, and uses thepublic domainEUREKA 147 (Band III) system. DAB is used mainly in the UK and South Africa. Germany and the Netherlands use the DAB and DAB+ systems, and France uses the L-Band system of DAB Digital Radio.
The broadcasting regulators of the United States and Canada have chosen to useHD radio, anin-band on-channel system that puts digital broadcasts at frequencies adjacent to the analog broadcast. HD Radio is owned by aconsortium of private companies that is callediBiquity. An internationalnon-profit consortiumDigital Radio Mondiale (DRM), has introduced thepublic domain DRM system, which is used by a relatively small number of broadcasters worldwide.
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Broadcasters in one country have several reasons to reach out to an audience in other countries. Commercial broadcasters may simply see a business opportunity to sell advertising or subscriptions to a broader audience. This is more efficient than broadcasting to a single country, because domestic entertainment programs and information gathered by domestic news staff can be cheaply repackaged for non-domestic audiences.
Governments typically have different motivations for funding international broadcasting. One clear reason is for ideological, orpropaganda reasons. Many government-owned stations portray their nation in a positive, non-threatening way. This could be to encourage business investment in or tourism to the nation. Another reason is to combat a negative image produced by other nations or internal dissidents, or insurgents.Radio RSA, the broadcasting arm of the apartheid South African government, is an example of this. A third reason is to promote the ideology of the broadcaster. For example, a program onRadio Moscow from the 1960s to the 1980s wasWhat is Communism?
A second reason is to advance a nation's foreign policy interests and agenda by disseminating its views on international affairs or on the events in particular parts of the world. During theCold War the AmericanRadio Free Europe andRadio Liberty and Indian RadioAIR were founded to broadcast news from "behind theIron Curtain" that was otherwise being censored and promote dissent and occasionally, to disseminatedisinformation. Currently, the US operates similar services aimed atCuba (Radio y Televisión Martí) and thePeople's Republic of China,Vietnam,Laos andNorth Korea (Radio Free Asia).
Besides ideological reasons, many stations are run by religious broadcasters and are used to provide religious education, religious music, or worship service programs. For example,Vatican Radio, established in 1931, broadcasts such programs. Another station, such asHCJB orTrans World Radio will carry brokered programming from evangelists. In the case of theBroadcasting Services of the Kingdom of Saudi Arabia, both governmental and religious programming is provided.
Extensions of traditional radio-wave broadcasting foraudio broadcasting in general includecable radio, local wiretelevision networks,DTV radio,satellite radio, andInternet radio viastreaming media on theInternet.
The enormous entry costs of space-based satellite transmitters and restrictions on availableradio spectrum licenses has restricted growth ofSatellite radio broadcasts. In the US andCanada, just two services,XM Satellite Radio andSirius Satellite Radio exist. Both XM and Sirius are owned bySirius XM Satellite Radio, which was formed by the merger of XM and Sirius on July 29, 2008, whereas inCanada,XM Radio Canada andSirius Canada remained separate companies until 2010.Worldspace in Africa and Asia, andMobaHO! in Japan and the ROK were two unsuccessful satellite radio operators which have gone out of business.
Radio program formats differ by country, regulation, and markets. For instance, the U.S.Federal Communications Commission designates the 88–92 megahertz band in the U.S. for non-profit or educational programming, with advertising prohibited.
In addition, formats change in popularity as time passes and technology improves. Early radio equipment only allowed program material to be broadcast in real time, known aslive broadcasting. As technology forsound recording improved, an increasing proportion of broadcast programming used pre-recorded material. A current trend is theautomation of radio stations. Some stations now operate without direct human intervention by using entirely pre-recorded material sequenced bycomputer control.
{{cite web}}: CS1 maint: bot: original URL status unknown (link) by James E. O'Neal,Radio World, October 25, 2006. (radioworld.com){{cite web}}: CS1 maint: bot: original URL status unknown (link) by James E. O'Neal,Radio World, December 23, 2008. (radioworld.com){{cite web}}: CS1 maint: bot: original URL status unknown (link), Joseph E. Baudino and John M. Kittross,Journal of Broadcasting, Winter 1977, page 62.
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